High-Speed Friction Stir Welding

Abstract

Contemplated systems and methods significantly improve friction stir welding of hard metals and particularly steel and stainless steel. Among other factors, the inventors found that high transverse velocity of the tool is critical to obtain predictable and desirable weld quality, which is preferably achieved in such materials by minimizing spindle run out. Moreover, the transverse and angular velocities are preferably selected such as to achieve a temperature in the weld that is below the phase change temperature and / or the solid state transformation point of the materials.

Description

[0001]This application claims priority to our U.S. provisional application with Ser. No. 61 / 079388, which was filed 09 Jul. 2008.FIELD OF THE INVENTION[0002]The field of the invention is friction stir welding.BACKGROUND OF THE INVENTION[0003]Friction stir welding (FSW) is an emerging method of fusing a variety of materials and provides numerous advantages over conventional welding methods. FSW is conceptually simple and typically does not require use of any filler metal or flux. As a result, a full strength bond can be achieved with optimal mechanical characteristics. Moreover, as friction stir welding is a solid state fusion process that occurs below the melting point of the material, problems associated with the heat affected zone, unwanted grain growth, shrinkage, and / or distortion can be reduced, if not even entirely avoided. Still further, FSW does in most cases not require post weld treatment. Even more advantageously, FSW provides an efficient and reliable way of joining sele...

AI Technical Summary

Benefits of technology

[0009]The present invention is directed to improved configurations and methods for FSW of relatively hard materials, and especially of steel and stainless steel materials. In especially preferred aspects of the inventive subject matter, the inventors identified and characterized certain process parameters in FSW critical to predictable and reproducible formation of stable welds in various steel materials. Most significantly, contemplated configurations and methods are characterized by an elevated transverse velocity (typically above 12 in / min) and use of a spindle with near-zero (typically less than 5×10E-4 inch) run out at zero load. Such methods and configurations significantly increase welding speed while producing reproducible welds with high integrity and strength.

Problems solved by technology

As relatively little is known about the specific contribution of one or more parameters in forming a stable weld between two materials, reliable and reproducible weld formation is often a matter of trial and error and the multitude of possible determinants will often preclude a rationale process design.

Unfortunately, while such known devices and methods tend to improve certain aspects of FSW, other difficulties often to arise.

For example, force controlled systems and methods frequently suffer from relatively slow transverse welding speed, and specific tool design typically limits the transverse force that can be applied, which results in slow welding speeds.

On the other hand, where the materials are preheated or heated with an external heater, difficulties may be encountered due to expansion, inadvertent overheating, etc.

Moreover, friction stir welding has generally only found acceptance and practical use with relatively soft or non-ferrous materials (e.g., aluminum, magnesium, copper, zinc, and lead alloys) as these materials become plastic at relatively low temperatures.

However, the use of friction stir welding of carbon steels or stainless steel has been limited by the lack of suitable tool materials that can withstand the high temperatures and pressures required to weld such harder materials.

Unfortunately, the transverse speed was undesirably low (at 1-4 in / min).

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